Light-emitting device

ABSTRACT

A light-emitting device of an embodiment of the present disclosure comprises a substrate; a semiconductor stack comprising a first type semiconductor layer, a second type semiconductor layer and an active layer formed between the first type semiconductor layer and the second type semiconductor layer, wherein the first type semiconductor layer comprises a non-planar roughened surface; a bonding layer formed between the substrate and the semiconductor stack; and multiple recesses each comprising a bottom surface lower than the non-planar roughened surface; and multiple buried electrodes physically buried in the first type semiconductor layer, wherein the multiple buried electrodes are formed in the multiple recesses respectively, and one of the multiple buried electrodes comprises an upper surface higher than the non-planar roughened surface of the first type semiconductor layer.

REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent application Ser. No. 13/421,898 entitled “LIGHT-EMITTING DEVICE”, filed on Mar. 16, 2012, the contents of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The application relates to a light-emitting device, and more particularly, to a light-emitting device with a plurality of buried electrodes.

DESCRIPTION OF BACKGROUND ART

The light-emitting diode (LED) is a solid state semiconductor device, which has been broadly used as a light-emitting device. The light-emitting device structure comprises a p-type semiconductor layer, an n-type semiconductor layer, and an active layer. The active layer is formed between the p-type semiconductor layer and the n-type semiconductor layer. The structure of the light-emitting device generally comprises III-V group compound semiconductor such as gallium phosphide, gallium arsenide, or gallium nitride. The light-emitting principle of the LED is the transformation of electrical energy to optical energy by applying electrical current to the p-n junction to generate electrons and holes. Then, the LED emits light when the electrons and the holes combine.

FIG. 1A illustrates a conventional light-emitting device 1 a. The light-emitting device 1 a comprises a substrate 15 a; a semiconductor stack 10 a comprising a first type semiconductor layer 13 a, a second type semiconductor layer 11 a and an active layer 12 a formed between the first type semiconductor layer 13 a and the second type semiconductor layer 11 a; a first electrode 18 a electrically connected to the first type semiconductor layer 13 a; and a second electrode 19 a electrically connected to the second type semiconductor layer 11 a. The material of the first electrode 18 a and the second electrode 19 a comprises metal or metal alloy. As illustrated in FIG. 1A, the first electrode 18 a is formed on a top surface 17 a of the light-emitting device 1 a. The electrical current from the first electrode 18 a is not dispersed uniformly in the first type semiconductor layer 13 a of the light-emitting device 1 a.

FIG. 1B illustrates another example of a conventional light-emitting device 1 b. The light-emitting device 1 b comprises a substrate 15 b; a semiconductor stack 10 b comprising a first type semiconductor layer 13 b, a second type semiconductor layer 11 b and an active layer 12 b formed between the first type semiconductor layer 13 b and the second type semiconductor layer 11 b; a first electrode 18 b electrically connected to the first type semiconductor layer 13 b; a second electrode 19 b electrically connected to the second type semiconductor layer 11 b; and a conductive layer 16 b formed between the first type semiconductor layer 13 b and the first electrode 18 b. The material of the first electrode 18 b and the second electrode 19 b comprises metal or metal alloy.

As illustrated in FIG. 1B, the conductive layer 16 b is formed on the first type semiconductor layer 13 b and the first electrode 18 b is formed on a top surface 17 b of the conductive layer 16 b. The material of the conductive layer 16 b comprises thin metal or metal alloy. The conductive layer 16 b is used to improve the electrical current spreading. However, the transmittance of the conductive layer 16 b is low, and the light emitting efficiency of the light-emitting device 1 b is affected.

SUMMARY OF THE DISCLOSURE

A light-emitting device of an embodiment of the present disclosure comprises a substrate; a semiconductor stack comprising a first type semiconductor layer, a second type semiconductor layer and an active layer formed between the first type semiconductor layer and the second type semiconductor layer, wherein the first type semiconductor layer comprises a non-planar roughened surface; a bonding layer formed between the substrate and the semiconductor stack; and multiple recesses each comprising a bottom surface lower than the non-planar roughened surface; and multiple buried electrodes physically buried in the first type semiconductor layer, wherein the multiple buried electrodes are formed in the multiple recesses respectively, and one of the multiple buried electrodes comprises an upper surface higher than the non-planar roughened surface of the first type semiconductor layer.

A light-emitting device of an embodiment of the present disclosure comprises a substrate; a semiconductor stack comprising a first type semiconductor layer, a second type semiconductor layer and an active layer formed between the first type semiconductor layer and the second type semiconductor layer wherein the first type semiconductor layer comprises a top surface; a bonding layer formed between the substrate and the semiconductor stack; multiple recesses recessed from the top surface toward the active layer; and multiple buried electrodes in the multiple recesses respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a cross-sectional diagram of a conventional light-emitting device;

FIG. 1B illustrates a cross-sectional diagram of a conventional light-emitting device;

FIG. 2 illustrates a cross-sectional diagram of a light-emitting device according to the first embodiment of the present disclosure;

FIGS. 3A to 3D illustrate a process flow for manufacturing the light-emitting device according to an embodiment of the present disclosure;

FIGS. 4A to 4C illustrate cross-sectional diagrams of a plurality of buried electrodes in a light-emitting device according to the first embodiment of the present disclosure;

FIGS. 5A to 5I illustrate cross-sectional diagrams of a plurality of buried electrodes in a light-emitting device according to the first embodiment of the present disclosure;

FIG. 6 illustrates a cross-sectional diagram of a light-emitting device according to the second embodiment of the present disclosure;

FIGS. 7A to 7B illustrate cross-sectional diagrams of a plurality of buried electrodes in a light-emitting device according to the second embodiment of the present disclosure;

FIG. 8 illustrates a cross-sectional diagram of a light-emitting device according to the third embodiment of the present disclosure; and

FIGS. 9A to 9B illustrate cross-sectional diagrams of a plurality of buried electrodes in a light-emitting device according to the third embodiment of the present disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The embodiment of the disclosure is illustrated in detail, and is plotted in the drawings. The same or the similar part is illustrated in the drawings and the specification with the same number.

FIG. 2 illustrates a cross-sectional diagram of a light-emitting device 2 according to the first embodiment of the present disclosure. The light-emitting device 2 comprises a substrate 27; a semiconductor stack 20 comprising a first type semiconductor layer 23, a second type semiconductor layer 21 and an active layer 22 formed between the first type semiconductor layer 23 and the second type semiconductor layer 21; a bonding layer 25 formed between the substrate 27 and the semiconductor stack 20; a first electrode 28 electrically connected to the first type semiconductor layer 23; a second electrode 29 electrically connected to the second type semiconductor layer 21; and a plurality of buried electrodes 24 physically buried in the first type semiconductor layer 23 and electrically connected to the first electrode 28.

The material of the semiconductor stack 20 comprises III-V group based semiconductor material such as InGaN, AlGaAs, or AlGaInP. The semiconductor stack 20 is epitaxially grown on a growth substrate (not shown). The method of forming each layer of the semiconductor stack 20 is not particularly limited. Besides a metal organic chemical vapor deposition method (MOCVD method), each layer of the semiconductor stack 20 may be formed by a known method such as a molecular beam epitaxy method (MBE method), a hydride vapor phase epitaxy method (HVPE method), a sputtering method, an ion-plating method and an electron showering method.

The plurality of buried electrodes 24 buried in the first type semiconductor layer 23 increases the contact area between the buried electrode 24 and the first type semiconductor layer 23. Each of the plurality of the buried electrode 24 electrically connected to each other with an extension electrode (not shown). With the buried electrode 24, the contact area between the buried electrode 24 and the first type semiconductor layer 23 is increased and an electrical current is injected into the first type semiconductor layer 23 uniformly.

A trench 200 is formed in the semiconductor stack 20 by etching process. A sidewall 200 a of the trench 200 is insulated from the semiconductor stack 20 with dielectric materials such as SiO₂ and Si₃N₄. A conductive channel is formed by filling conductive material in the trench 200, wherein the conductive material can be metal or metal alloy, or a transparent conductive material like ITO or ZnO. The materials of the plurality of buried electrodes 24 and the first electrode 28 comprise conductive materials such as metal or metal alloy, and transparent conductive materials such as ITO or ZnO. The materials of the plurality of buried electrodes 24, the first electrode 28 and the trench 200 are the same or different from each other. The plurality of buried electrodes 24 and the first electrode 28 are electrically connected via the conductive channel. The first electrode 28 and the second electrode 29 are formed on the same side of the semiconductor stack 20 opposite to a top surface 23 a of the first type semiconductor layer 23. The first electrode 28 and the second electrode 29 are isolated from each other by an isolation layer 200 b. The material of the isolation layer 200 b comprises dielectric material such as SiO₂ and Si₃N₄.

As shown in FIG. 2, the substrate 27 is a transparent substrate. A light emitted from the active layer 22 can be emitted out through the transparent substrate 27. The material of the substrate 27 can be sapphire, glass, GaP, ZnSe and SiC. The substrate 27 is attached to the first type semiconductor layer 23 by the bonding layer 25. The material of the bonding layer 25 can be transparent material such as epoxy, polyimide (PI), perfluorocyclobutane (PFCB), benzocyclobutene (BCB), spin-on glass (SOG) and silicone.

When the light-emitting device 2 is operated under a high electrical current, the thickness of the buried electrode 24 is preferred to be thick with a range of about 2˜6 μm to reduce the sheet resistance of the light-emitting device 2 and increase the device reliability. As shown in FIG. 2, when the light emitted from the active layer 22 passes through the bonding layer 25, part of the light is absorbed by the bonding layer 25. In order to reduce the thickness H2 a of the bonding layer 25, improve the light emission efficiency of the light-emitting device 2 and maintain the thickness of the buried electrode 24 in a range of about 2˜6 μm, the plurality of buried electrodes 24 is buried in the first type semiconductor layer 23. The first type semiconductor layer 23 comprises the top surface 23 a and a plurality of recesses 24 a. Each of the plurality of recesses 24 a comprises a bottom surface 24 b lower than the top surface 23 a of the first type semiconductor layer 23. The conductive materials such as metal or metal alloy, or the transparent conductive materials such as ITO or ZnO are formed in the plurality of recesses 24 a to form the plurality of buried electrodes 24. The conductive materials or the transparent conductive materials can be formed in the plurality of recesses 24 a by electron beam evaporation, physical vapor deposition or sputter deposition.

FIGS. 3A-3D illustrate a process flow for manufacturing a light-emitting device 3 according to an embodiment of the present disclosure. As shown in FIGS. 3A-3D, a photoresist layer 31 formed on a top surface 35 of a semiconductor stack 30 is used to define the pattern of a plurality of buried electrodes 34 of the light-emitting device 3 by a conventional lithography process. As shown in FIG. 3B, a plurality of recesses 37 is formed by etching the semiconductor stack 30 through an area 32 not protected by the photoresist layer 31. A depth D2 of each of the plurality of recesses 37 is controlled by dry etching process parameters such as etch time, etchant gas flow rate and etchant gas type. A wet etch process is optionally performed to clean the surface containments of the plurality of recesses 37, and flatten a sidewall surface 37 s and a bottom surface 37 b of each of the plurality of recesses 37. As shown in FIG. 3C, a conductive material 33 is formed in the plurality of recesses 37 and on a top surface 36 of the photoresist layer 31. The adhesion between the semiconductor stack 30 and the conductive material 33 is improved because of the flat sidewall surface 37 s and bottom surface 37 b of each of the plurality of recesses 37. As shown in FIG. 3D, the photoresist layer 31 is lifted off by the conventional etch method and the plurality of buried electrodes 34 is buried in the semiconductor stack 30. The thickness T3 of each of the plurality of buried electrodes 34 is controlled by thin-film deposition process such as deposition rate and deposition time. After the pattern definition process and the deposition process as shown in FIGS. 3A-3D are finished, the plurality of buried electrodes 34 comprising an upper surface 341 is formed in the plurality of recesses 37 correspondingly.

As shown in FIG. 2, the plurality of buried electrodes 24 is buried in the first type semiconductor layer 23 by the method illustrated in FIGS. 3A-3D. Each of the plurality of buried electrodes 24 comprises an embedded portion 242 formed under the top surface 23 a of the first type semiconductor layer 23 and an exposed portion 241 formed above the top surface 23 a of the first type semiconductor layer 23. The embedded portion 242 is physically buried in the first type semiconductor layer 23 and electrically connected to the first type semiconductor layer 23. The thickness H2 of the exposed portion of each of the plurality of buried electrodes 24 is reduced compared with that of the electrode not buried in the first type semiconductor layer. Because the thickness H2 of the exposed portion of each of the plurality of buried electrodes 24 is reduced, the thickness H2 a of the bonding layer 25 used to attach the substrate 27 to the semiconductor stack 20 is also reduced.

The thickness H2 a of the bonding layer 25 is related with the thickness H2 of the exposed portion 241 of each of the plurality of buried electrodes 24. As the thickness H2 of the exposed portion 241 is increased, the thickness H2 a of the bonding layer 25 is preferred to be increased to provide adhesion between the substrate 27 and the semiconductor stack 20. FIGS. 4A-4C illustrate different examples of the plurality of buried electrodes 24 in the light-emitting device 2 according to the first embodiment of the present disclosure.

FIG. 4A illustrates an example of a cross-sectional diagram of the plurality of buried electrodes 24 in the light-emitting device 2 according to the first embodiment of the present disclosure. As shown in FIG. 4A, an upper surface 443 of each of the plurality of buried electrodes 24 is higher than the top surface 23 a of the first type semiconductor layer 23. Each of the plurality of buried electrodes 24 comprises the embedded portion 242 formed under the top surface 23 a of the first type semiconductor layer 23 and the exposed portion 241 formed above the top surface 23 a of the first type semiconductor layer 23. The size of the embedded portion 242 is smaller than that of the exposed portion 241.

FIG. 4B illustrates another example of a cross-sectional diagram of the plurality of buried electrodes 24 in the light-emitting device 2 according to the first embodiment of the present disclosure. The size of the embedded portion 242 is equal to that of the exposed portion 241.

FIG. 4C illustrates another example of a cross-sectional diagram of the plurality of buried electrodes 24 in the light-emitting device 2 according to the first embodiment of the present disclosure. The size of the embedded portion 242 is larger than that of the exposed portion 241.

As shown in FIG. 2, in order to increase the light emission efficiency of the light-emitting device 2, the top surface 23 a of the first type semiconductor layer 23 can be a non-planar surface such as the one of the cross-sectional diagrams illustrated in FIGS. 5A-5I.

FIG. 5A illustrates an example of a cross-sectional diagram of the plurality of buried electrodes 24 in the light-emitting device 2 according to the first embodiment of the present disclosure. The top surface 23 a of the first type semiconductor layer 23 is a non-planar surface. In the present embodiment, the non-planar surface is a roughened surface 23 a′, and an average roughness of the roughened surface 23 a′ is greater than 0.05 μm. The light emission efficiency of the light-emitting device 2 illustrated in FIG. 2 is increased by the roughened surface 23 a′. As shown in FIG. 5A, the upper surface 443 of each of the plurality of buried electrodes 24 is higher than the roughened surface 23 a′ of the first type semiconductor layer 23. Each of the plurality of buried electrodes 24 comprises the embedded portion 242 formed under the top surface 23 a of the first type semiconductor layer 23 and the exposed portion 241 formed above the top surface 23 a of the first type semiconductor layer 23. The embedded portion 242 is physically buried in the first type semiconductor layer 23 and electrically connected to the first type semiconductor layer 23. The size of the embedded portion 242 is smaller than that of the exposed portion 241.

FIG. 5B illustrates another example of a cross-sectional diagram of the plurality of buried electrodes 24 in the light-emitting device 2 according to the first embodiment of the present disclosure. The top surface 23 a of the first type semiconductor layer 23 is the non-planar surface. In the present embodiment, the non-planar surface is the roughened surface 23 a′, and the average roughness of the roughened surface 23 a′ is greater than 0.05 μm. The light emission efficiency of the light-emitting device 2 is increased by the roughened surface 23 a′. As shown in FIG. 5B, the upper surface 443 of each of the plurality of buried electrodes 24 is higher than the roughened surface 23 a′ of the first type semiconductor layer 23. Each of the plurality of buried electrodes 24 comprises the embedded portion 242 formed under the top surface 23 a of the first type semiconductor layer 23 and the exposed portion 241 formed above the top surface 23 a of the first type semiconductor layer 23. The embedded portion 242 is physically buried in the first type semiconductor layer 23 and electrically connected to the first type semiconductor layer 23. The size of the embedded portion 242 is equal to that of the exposed portion 241.

FIG. 5C illustrates another example of a cross-sectional diagram of the plurality of buried electrodes 24 in the light-emitting device 2 according to the first embodiment of the present disclosure. The top surface 23 a of the first type semiconductor layer 23 is the non-planar surface. In the embodiment, the non-planar surface is the roughened surface 23 a′, and the average roughness of the roughened surface 23 a′ is greater than 0.05 μm. The light emission efficiency of the light-emitting device 2 is increased by the roughened surface 23 a′. As shown in FIG. 5C, the upper surface 443 of each of the plurality of buried electrodes 24 is higher than the roughened surface 23 a′ of the first type semiconductor layer 23. Each of the plurality of buried electrodes 24 comprises the embedded portion 242 formed under the top surface 23 a of the first type semiconductor layer 23 and the exposed portion 241 formed above the top surface 23 a of the first type semiconductor layer 23. The embedded portion 242 is physically buried in the first type semiconductor layer 23 and electrically connected to the first type semiconductor layer 23. The size of the embedded portion 242 is larger than that of the exposed portion 241.

When the top surface 23 a of the first type semiconductor layer 23 is the roughened surface 23 a′ and the upper surface 443 of each of the plurality of buried electrodes 24 is higher than the roughened surface 23 a′ of the first type semiconductor layer 23 as illustrated in FIGS. 5A-5C, the thickness H2 a of the bonding layer 25 is determined according to the thickness H2 of the exposed portion 241.

FIG. 5D illustrates another example of a cross-sectional diagram of the plurality of buried electrodes 24 in the light-emitting device 2 according to the first embodiment of the present disclosure. The top surface 23 a of the first type semiconductor layer 23 is the non-planar surface. In the present embodiment, the non-planar surface is the roughened surface 23 a′, and the average roughness of the roughened surface 23 a′ is greater than 0.05 μm. The light emission efficiency of the light-emitting device 2 is increased by the roughened surface 23 a′. As shown in FIG. 5D, the upper surface 443 of each of the plurality of buried electrodes 24 and the roughened surface 23 a′ of the first type semiconductor layer 23 are substantially on the same plane. Each of the plurality of buried electrodes 24 comprises the embedded portion 242 formed under the top surface 23 a of the first type semiconductor layer 23 and the exposed portion 241 formed above the top surface 23 a of the first type semiconductor layer 23. The embedded portion 242 is physically buried in the first type semiconductor layer 23 and electrically connected to the first type semiconductor layer 23. The size of the embedded portion 242 is smaller than that of the exposed portion 241.

FIG. 5E illustrates another example of a cross-sectional diagram of the plurality of buried electrodes 24 in the light-emitting device 2 according to the first embodiment of the present disclosure. The top surface 23 a of the first type semiconductor layer 23 is the non-planar surface. In the present disclosure, the non-planar surface is the roughened surface 23 a′, and the average roughness of the roughened surface 23 a′ is greater than 0.05 μm. The light emission efficiency of the light-emitting device 2 is increased by the roughened surface 23 a′. As shown in FIG. 5E, the upper surface 443 of each of the plurality of buried electrodes 24 and the roughened surface 23 a′ of the first type semiconductor layer 23 are substantially on the same plane. Each of the plurality of buried electrodes 24 comprises the embedded portion 242 formed under the top surface 23 a of the first type semiconductor layer 23 and the exposed portion 241 formed above the top surface 23 a of the first type semiconductor layer 23. The embedded portion 242 is physically buried in the first type semiconductor layer 23 and electrically connected to the first type semiconductor layer 23. The size of the embedded portion 242 is larger than that of the exposed portion 241.

FIG. 5F illustrates another example of a cross-sectional diagram of the plurality of buried electrodes 24 in the light-emitting device 2 according to the first embodiment of the present disclosure. The top surface 23 a of the first type semiconductor layer 23 is the non-planar surface. In the present embodiment, the non-planar surface is the roughened surface 23 a′, and the average roughness of the roughened surface 23 a′ is greater than 0.05 μm. The light emission efficiency of the light-emitting device 2 is increased by the roughened surface 23 a′. As shown in FIG. 5F, the upper surface 443 of each of the plurality of buried electrodes 24 and the roughened surface 23 a′ of the first type semiconductor layer 23 are substantially on the same plane. Each of the plurality of buried electrodes 24 comprises the embedded portion 242 formed under the top surface 23 a of the first type semiconductor layer 23 and the exposed portion 241 formed above the top surface 23 a of the first type semiconductor layer 23. The embedded portion 242 is physically buried in the first type semiconductor layer 23 and electrically connected to the first type semiconductor layer 23. The size of the embedded portion 242 is equal to that of the exposed portion 241.

When the top surface 23 a of the first type semiconductor layer 23 is the roughened surface 23 a′, and the upper surface 443 of each of the plurality of buried electrodes 24 and the roughened surface 23 a′ of the first type semiconductor layer 23 are substantially on the same plane as illustrated in FIGS. 5D-5F, the thickness H2 a of the bonding layer 25 is preferred at least larger than 0.05 μm.

FIG. 5G illustrates another example of a cross-sectional diagram of the plurality of buried electrodes 24 in the light-emitting device 2 according to the first embodiment of the present disclosure. The top surface 23 a of the first type semiconductor layer 23 is the non-planar surface. In the present embodiment, the non-planar surface is the roughened surface 23 a′, and the average roughness of the roughened surface 23 a′ is greater than 0.05 μm. The light emission efficiency of the light-emitting device 2 is increased by the roughened surface 23 a′. As shown in FIG. 5G, the upper surface 443 of each of the plurality of buried electrodes 24 is lower than the roughened surface 23 a′ of the first type semiconductor layer 23. Each of the plurality of buried electrodes 24 comprises the embedded portion 242 formed under the top surface 23 a of the first type semiconductor layer 23 and the exposed portion 241 formed above the top surface 23 a of the first type semiconductor layer 23. The embedded portion 242 is physically buried in the first type semiconductor layer 23 and electrically connected to the first type semiconductor layer 23. The size of the embedded portion 242 is smaller than that of the exposed portion 241.

FIG. 5H illustrates another example of a cross-sectional diagram of the plurality of buried electrodes 24 in the light-emitting device 2 according to the first embodiment of the present disclosure. The top surface 23 a of the first type semiconductor layer 23 is the non-planar surface. In the present embodiment, the non-planar surface is the roughened surface 23 a′, and the average roughness of the roughened surface 23 a′ is greater than 0.05 μm. The light emission efficiency of the light-emitting device 2 is increased by the roughened surface 23 a′. As shown in FIG. 5H, the upper surface 443 of each of the plurality of buried electrodes 24 is lower than the roughened surface 23 a′ of the first type semiconductor layer 23. Each of the plurality of buried electrodes 24 comprises the embedded portion 242 formed under the top surface 23 a of the first type semiconductor layer 23 and the exposed portion 241 formed above the top surface 23 a of the first type semiconductor layer 23. The embedded portion 242 is physically buried in the first type semiconductor layer 23 and electrically connected to the first type semiconductor layer 23. The size of the embedded portion 242 is equal to that of the exposed portion 241.

FIG. 5I illustrates another example of a cross-sectional diagram of the plurality of buried electrodes 24 in the light-emitting device 2 according to the first embodiment of the present disclosure. The top surface 23 a of the first type semiconductor layer 23 is the non-planar surface. In the present embodiment, the non-planar surface is the roughened surface 23 a′, and the average roughness of the roughened surface 23 a′ is greater than 0.05 μm. The light emission efficiency of the light-emitting device 2 is increased by the roughened surface 23 a′. As shown in FIG. 5I, the upper surface 443 of each of the plurality of buried electrodes 24 is lower than the roughened surface 23 a′ of the first type semiconductor layer 23. Each of the plurality of buried electrodes 24 comprises the embedded portion 242 formed under the top surface 23 a of the first type semiconductor layer 23 and the exposed portion 241 formed above the top surface 23 a of the first type semiconductor layer 23. The embedded portion 242 is physically buried in the first type semiconductor layer 23 and electrically connected to the first type semiconductor layer 23. The size of the embedded portion 242 is larger than that of the exposed portion 241.

When the top surface 23 a of the first type semiconductor layer 23 is the roughened surface 23 a′ and the upper surface 443 of each of the plurality of buried electrodes 24 is lower than the roughened surface 23 a′ of the first type semiconductor layer 23 as illustrated in FIGS. 5G-5I, the thickness H2 a of the bonding layer 25 is preferred at least larger than 0.05 μm.

FIG. 6 illustrates a cross-sectional diagram of a light-emitting device 6 according to the second embodiment of the present disclosure. The light-emitting device 6 comprises a substrate 67; a semiconductor stack 60 comprising a first type semiconductor layer 63, a second type semiconductor layer 61, and an active layer 62 formed between the first type semiconductor layer 63 and the second type semiconductor layer 61; a bonding layer 65 formed between the substrate 67 and the semiconductor stack 60; a first electrode 68 electrically connected to the first type semiconductor layer 63; a second electrode 69 electrically connected to the second type semiconductor layer 61; and a plurality of buried electrodes 64 physically buried in the first type semiconductor layer 63 and electrically connected to the first electrode 68.

The material of the semiconductor stack 60 comprises III-V group based semiconductor material such as InGaN, AlGaAs, or AlGaInP. The semiconductor stack 60 is epitaxially grown on a growth substrate (not shown). The method of forming each layer of the semiconductor stack 60 is not particularly limited. Besides a metal organic chemical vapor deposition method (MOCVD method), each layer of the semiconductor stack 60 may be formed by a known method such as a molecular beam epitaxy method (MBE method), a hydride vapor phase epitaxy method (HVPE method), a sputtering method, an ion-plating method and an electron showering method.

The plurality of buried electrodes 64 buried in the first type semiconductor layer 63 increases the contact area between the buried electrode 64 and the first type semiconductor layer 63. Each of the plurality of the buried electrode 64 electrically connected to each other with an extension electrode (not shown). With the buried electrode 64, the contact area between the buried electrode 64 and the first type semiconductor layer 63 is increased and an electrical current is injected into the first type semiconductor layer 63 uniformly.

A trench 600 is formed in the semiconductor stack 60 by etching process. A sidewall 600 a of the trench 600 is insulated from the semiconductor stack 60 with dielectric materials such as SiO₂ or Si₃N₄. A conductive channel is formed by filling conductive material in the trench 600, wherein the conductive material can be metal or metal alloy, or a transparent conductive material like ITO or ZnO. The materials of the plurality of buried electrodes 64 and the first electrode 68 comprise conductive materials such as metal or metal alloy, and transparent conductive materials such as ITO or ZnO. The materials of the plurality of buried electrodes 64, the first electrode 68 and the trench 600 are the same or different from each other. The plurality of buried electrodes 64 and the first electrode 68 are electrically connected via the conductive channel. In the present embodiment, the first electrode 68 and the second electrode 69 are formed on the same side of the semiconductor stack 60 opposite to a top surface 63 a of the first type semiconductor 63. The first electrode 68 and the second electrode 69 are isolated from each other by an isolation layer 600 b. The material of the isolation layer 600 b comprises dielectric material such as SiO₂ or Si₃N₄.

As shown in FIG. 6, the substrate 67 is a transparent substrate. A light emitted from the active layer 62 can be emitted out through the transparent substrate 67. The material of the substrate 67 can be sapphire, glass, GaP, ZnSe, and SiC. The substrate 67 is attached to the first type semiconductor layer 63 by the bonding layer 65. The material of the bonding layer 65 can be transparent material such as epoxy, polyimide (PI), perfluorocyclobutane (PFCB), benzocyclobutene (BCB), spin-on glass (SOG) and silicone.

When the light-emitting device 6 is operated under a high electrical current, the thickness of the buried electrode 64 is preferred to be thick with a range of about 2˜6 μm to reduce the sheet resistance of the light-emitting device 6 and increase the device reliability. As shown in FIG. 6, when the light emitted from the active layer 62 passes through the bonding layer 65, part of the light is absorbed by the bonding layer 65. In order to reduce the thickness H6 a of the bonding layer 65, improve the light emission efficiency of the light-emitting device 6, and maintain the thickness of the buried electrode 64 in a range of about 2˜6 μm, the plurality of buried electrodes 64 is buried in the first type semiconductor layer 63. The first type semiconductor layer 63 comprises the top surface 63 a and a plurality of recesses 64 a. Each of the plurality of recesses 64 a comprises a bottom surface 64 b lower than the top surface 63 a of the first type semiconductor layer 63. The conductive materials such as metal or metal alloy, or the transparent conductive materials such as ITO or ZnO are formed in the plurality of recesses 64 a to form the plurality of buried electrodes 64. The conductive materials or the transparent conductive materials can be formed in the plurality of recesses 64 a by electron beam evaporation, physical vapor deposition or sputter deposition. The upper surface 64 c of each of the plurality of the buried electrodes 64 and the top surface 63 a of the first type semiconductor layer 63 are substantially on the same plane.

FIG. 7A illustrates an example of a cross-sectional diagram of the plurality of buried electrodes 64 in the light-emitting device 6 according to the second embodiment of the present disclosure. As shown in FIG. 7A, the first type semiconductor layer 63 comprises the top surface 63 a and the plurality of recesses 64 a. Each of the plurality of recesses 64 a comprises the bottom surface 64 b lower than the top surface 63 a of the first type semiconductor layer 63. The conductive materials such as metal or metal alloy, and the transparent conductive materials such as ITO or ZnO are formed in the plurality of recesses 64 a to form the plurality of buried electrodes 64. The upper surface 64 c of each of the plurality of buried electrodes 64 and the top surface 63 a of the first type semiconductor layer 63 are substantially on the same plane.

As shown in FIG. 6, in order to increase the light emission efficiency of the light-emitting device 6, the top surface 63 a of the first type semiconductor layer 63 can be a non-planar surface as illustrated in FIG. 7B. FIG. 7B illustrates a cross-sectional diagram of the plurality of buried electrodes 64 in the light-emitting device 6 according to the second embodiment of the present disclosure. As shown in FIG. 7B, the first type semiconductor layer 63 comprises the top surface 63 a and the plurality of recesses 64 a. The top surface 63 a is a non-planar surface. The non-planar surface is a roughened surface 63 a′ and an average roughness of the roughened surface is greater than 0.05 μm. The light emission efficiency of the light-emitting device 6 is increased by the roughened surface 63 a′. Each of the plurality of recesses 64 a comprises the bottom surface 64 b lower than the top surface 63 a of the first type semiconductor layer 63. The conductive materials such as metal or metal alloy, and the transparent conductive materials such as ITO or ZnO are formed in the plurality of recesses 64 a to form the plurality of buried electrodes 64. The upper surface 64 c of each of the plurality of the buried electrodes 64 is lower than the roughened surface 63 a′ of the first type semiconductor layer 63.

As shown in FIG. 6, the plurality of buried electrodes 64 is totally buried in the first type semiconductor layer 63. The top surface 63 a of the first type semiconductor layer 63 and the upper surface 64 c of each of the plurality of the buried electrode 64 are substantially on the same plane. In the second embodiment illustrated in FIG. 6, the plurality of buried electrodes 64 is totally buried in the first type semiconductor layer 63 and there is no exposed portion of each of the plurality of buried electrodes 64. Thus, the thickness H6 a of the bonding layer 65 used to attach the substrate 67 to the semiconductor stack 60 is reduced.

FIG. 8 illustrates a cross-sectional diagram of a light-emitting device 8 according to the third embodiment of the present disclosure. The light-emitting device 8 comprises a substrate 87; a semiconductor stack 80 comprising a first type semiconductor layer 83, a second type semiconductor layer 81, and an active layer 82 formed between the first type semiconductor layer 83 and the second type semiconductor layer 81; a bonding layer 85 formed between the substrate 87 and the semiconductor stack 80; a first electrode 88 electrically connected to the first type semiconductor layer 83; a second electrode 89 electrically connected to the second type semiconductor layer 81; and a plurality of buried electrodes 84 physically buried in the first type semiconductor layer 83 and electrically connected to the first electrode 88.

The material of the semiconductor stack 80 comprises III-V group based semiconductor material such as InGaN, AlGaAs, or AlGaInP. The semiconductor stack 80 is epitaxially grown on a growth substrate (not shown). The method of forming each layer of the semiconductor stack 80 is not particularly limited. Besides a metal organic chemical vapor deposition method (MOCVD method), each layer of the semiconductor stack 80 may be formed by a known method such as a molecular beam epitaxy method (MBE method), a hydride vapor phase epitaxy method (HVPE method), a sputtering method, an ion-plating method and an electron showering method.

The plurality of buried electrodes 84 buried in the first type semiconductor layer 83 increases the contact area between the buried electrode 84 and the first type semiconductor layer 83. Each of the plurality of the buried electrode 84 electrically connected to each other with an extension electrode (not shown). With the buried electrode 84, the contact area between the buried electrode 84 and the first type semiconductor layer 83 is increased and an electrical current is injected into the first type semiconductor layer 83 uniformly.

A trench 800 is formed in the semiconductor stack 80 by etching process. A sidewall 800 a of the trench 800 is insulated from the semiconductor stack 80 with dielectric materials such as SiO₂ or Si₃N₄. A conductive channel is formed by filling conductive material in the trench 800, wherein the conductive material can be metal or metal alloy, or a transparent conductive material like ITO or ZnO. The materials of the plurality of buried electrodes 84 and the first electrode 88 comprise conductive materials such as metal or metal alloy, and transparent conductive materials such as ITO or ZnO. The materials of the plurality of buried electrodes 84, the first electrode 88 and the trench 800 are the same or different from each other. The plurality of buried electrodes 84 and the first electrode 88 are electrically connected via the conductive channel. The first electrode 88 and the second electrode 89 are formed on the same side of the semiconductor stack 80 opposite to a top surface 83 a of the first type semiconductor 83. The first electrode 88 and the second electrode 89 are isolated from each other by an isolation layer 800 b. The material of the isolation layer 800 b comprises dielectric material such as SiO₂ or Si₃N₄.

As shown in FIG. 8, the substrate 87 is a transparent substrate. A light emitted from the active layer 82 can be emitted out through the transparent substrate 87. The material of the substrate 87 can be sapphire, glass, GaP, ZnSe, and SiC. The substrate 87 is attached to the first type semiconductor layer 83 by the bonding layer 85. The material of the bonding layer 85 can be transparent material such as epoxy, polyimide (PI), perfluorocyclobutane (PFCB), benzocyclobutene (BCB), spin-on glass (SOG) and silicone.

When the light-emitting device 8 is operated under a high electrical current, the thickness of the buried electrode 84 is preferred to be thick with a range of about 2˜6 μm to reduce the sheet resistance of the light-emitting device 8 and increase the device reliability. As shown in FIG. 8, when the light emitted from the active layer 82 passes through the bonding layer 85, part of the light is absorbed by the bonding layer 85. In order to reduce the thickness H8 a of the bonding layer 85, improve the light emission efficiency of the light-emitting device 8, and maintain the thickness of the buried electrode 84 in a range of about 2˜6 μm, the plurality of buried electrodes 84 is buried in the first type semiconductor layer 83. The first type semiconductor layer 83 comprises the top surface 83 a and a plurality of recesses 84 a. Each of the plurality of recesses 84 a comprises a bottom surface 84 b lower than the top surface 83 a of the first type semiconductor layer 83. The conductive materials such as metal or metal alloy, or the transparent conductive materials such as ITO or ZnO are formed in the plurality of recesses 84 a to form the plurality of buried electrodes 84. The conductive materials or the transparent conductive materials can be formed in the plurality of recesses 84 a by electron beam evaporation, physical vapor deposition or sputter deposition. The upper surface 84 c of the buried electrode 84 is lower than the top surface 83 a of the first type semiconductor layer 83.

The plurality of buried electrodes 84 is buried in the first type semiconductor layer 83. FIG. 9A illustrates a cross-sectional diagram of the plurality of buried electrodes 84 in the light-emitting device 8 according to the third embodiment of the present disclosure. As shown in FIG. 9A, the first type semiconductor layer 83 comprises the top surface 83 a and the plurality of recesses 84 a. Each of the plurality of recesses 84 a comprises the bottom surface 84 b lower than the top surface 83 a of the first type semiconductor layer 83. The conductive materials such as metal or metal alloy, and the transparent conductive materials such as ITO or ZnO are formed in the plurality of recesses 84 a to form the plurality of buried electrodes 84. The upper surface 84 c of the buried electrode 84 is lower than the top surface 83 a of the first type semiconductor layer 83.

As shown in FIG. 8, in order to increase the light emission efficiency of the light-emitting device 8, the top surface 83 a of the first type semiconductor layer 83 can be a non-planar surface as illustrated in FIG. 9B. FIG. 9B illustrates a cross-sectional diagram of the plurality of buried electrodes 84 in the light-emitting device 8 according to the third embodiment of the present disclosure. As shown in FIG. 9B, the first type semiconductor layer 83 comprises the top surface 83 a and the plurality of recesses 84 a. The top surface 83 a is a non-planar surface. The non-planar surface is a roughened surface 83 a′ and an average roughness of the roughened surface 83 a′ is greater than 0.05 μm. The light emission efficiency of the light-emitting device 8 is increased by the roughened surface 83 a′. Each of the plurality of recesses 84 a comprises the bottom surface 84 b lower than the top surface 83 a of the first type semiconductor layer 83. The conductive materials such as metal or metal alloy, and the transparent conductive materials such as ITO or ZnO are formed in the plurality of recesses 84 a to form the plurality of buried electrodes 84. The upper surface 84 c of each of the plurality of the buried electrode 84 is lower than the roughened surface 83 a′ of the first type semiconductor layer 83.

As shown in FIG. 8, the plurality of buried electrodes 84 is totally buried in the first type semiconductor layer 83. The upper surface 84 c of the buried electrode 84 is lower than the top surface 83 a of the first type semiconductor layer 83. In the third embodiment illustrated in FIG. 8, the plurality of buried electrodes 84 is totally buried in the first type semiconductor layer 83 and there is no exposed portion of each of the plurality of buried electrodes 84. Thus, the thickness H8 a of the bonding layer 85 used to attach the substrate 87 to the semiconductor stack 80 is reduced.

The principle and the efficiency of the present disclosure illustrated by the embodiments above are not the limitation of the disclosure. Any person having ordinary skill in the art can modify or change the aforementioned embodiments. Therefore, the protection range of the rights in the disclosure will be listed as the following claims. 

What is claimed is:
 1. A light-emitting device, comprising: a substrate; a semiconductor stack comprising a first type semiconductor layer, a second type semiconductor layer and an active layer formed between the first type semiconductor layer and the second type semiconductor layer, wherein the first type semiconductor layer comprises a non-planar roughened surface; a bonding layer formed between the substrate and the semiconductor stack; and multiple recesses each comprising a bottom surface lower than the non-planar roughened surface; and multiple buried electrodes physically buried in the first type semiconductor layer, wherein the multiple buried electrodes are formed in the multiple recesses respectively, and one of the multiple buried electrodes comprises an upper surface higher than the non-planar roughened surface of the first type semiconductor layer.
 2. The light-emitting device according to claim 1, wherein one of the multiple buried electrodes comprises an embedded portion under the non-planar roughened surface of the first type semiconductor layer and an exposed portion above the non-planar roughened surface of the first type semiconductor layer.
 3. The light-emitting device according to claim 2, wherein the size of the embedded portion is larger than that of the exposed portion.
 4. The light-emitting device according to claim 2, wherein the embedded portion is electrically connected to the semiconductor stack.
 5. The light-emitting device according to claim 1, wherein an average roughness of the non-planar roughened surface is greater than 0.05 μm.
 6. The light-emitting device according to claim 1, wherein one of the multiple buried electrodes comprises metal or metal alloy.
 7. The light-emitting device according to claim 1, wherein the bottom surface is planar.
 8. The light-emitting device according to claim 1, wherein a thickness of one of the multiple buried electrode is in a range of about 2˜6 μm.
 9. The light-emitting device according to claim 1, wherein the material of the semiconductor stack comprises InGaN, AlGaAs, or AlGaInP.
 10. A light-emitting device, comprising: a substrate; a semiconductor stack comprising a first type semiconductor layer, a second type semiconductor layer and an active layer formed between the first type semiconductor layer and the second type semiconductor layer wherein the first type semiconductor layer comprises a top surface; a bonding layer formed between the substrate and the semiconductor stack; multiple recesses recessed from the top surface toward the active layer; and multiple buried electrodes in the multiple recesses respectively.
 11. The light-emitting device according to claim 10, wherein an upper surface of one of the multiple buried electrodes is higher than the top surface of the first type semiconductor layer.
 12. The light-emitting device according to claim 10, wherein one of the multiple recesses comprises a bottom surface lower than the top surface of the first type semiconductor layer, and the bottom surface is planar.
 13. The light-emitting device according to claim 10, wherein one of the multiple buried electrodes comprises an embedded portion fully embedded in one of the multiple recesses and an exposed portion protruded out of the top surface of the first type semiconductor layer.
 14. The light-emitting device according to claim 13, wherein the size of the embedded portion is larger than that of the exposed portion.
 15. The light-emitting device according to claim 13, wherein the embedded portion is electrically connected to the semiconductor stack.
 16. The light-emitting device according to claim 10, wherein the top surface of the first type semiconductor layer is a roughened surface.
 17. The light-emitting device according to claim 16, wherein an average roughness of the roughened surface is greater than 0.05 μm.
 18. The light-emitting device according to claim 10, wherein one of the multiple buried electrodes comprises metal or metal alloy.
 19. The light-emitting device according to claim 10, wherein the thickness of one of the multiple buried electrode is in a range of about 2˜6 μm.
 20. The light-emitting device according to claim 10, wherein the material of the semiconductor stack comprises InGaN, AlGaAs, or AlGaInP. 